He's right. We don't have that luxury – not only because the Kyoto protocol's first phase, running to 2012, is manifestly failing, but because the emissions reduction approach that it embodies cannot succeed. It is manifestly failing because emissions are going ahead faster than even the worst scenarios considered by the IPCC, which provides scientific assessments to the UN Climate Convention and because many rich countries are on course to fall short of their emissions reductions commitments.

Research since the IPCC's last assessment reveals that the threat of climatic disaster is more serious than previously supposed. Several threats exist but the most imminent is probably a collapse of substantial areas of land-based ice into the oceans, as studies of ancient climates show happened in previous warming phases. This seems likely to be due to the lubrication of Greenland's ice floes by water that accumulates year after year, with warmer summers melting the surface and rivers of melt-water flowing down crevasses to the bedrock, making the underside of the ice increasingly mushy and prone to slip down towards the ocean. Reports from Greenland, of increased frequency of "ice-quakes", suggest that areas of the ice cover have slipped and bumped into other areas that are still stuck. When the last bit gives way there may be an unstoppable rush of ice into the ocean, as with ancient warming phases, raising ocean levels by several metres over a few decades.

"Probably"? "Likely"? "Suggest"? "Maybe"? Yes, all is uncertain and the models are inadequate. But you don't drive full-speed down a twisty lane on a foggy winter's night hoping there's no ice round the next bend. A measure of the threat is the accumulation of warmth from successive summers, which is making the glaciers' undersides increasingly mushy. Even a deeply implausible reduction of emissions to zero in 25 years sees that measure treble over the next half-century with no end in sight.

So something more than emissions reductions is needed. We must take CO2 out of the atmosphere or prevent some of the sun's radiation from reaching the surface. But geo-engineering is usually thought of as shielding the earth from solar radiation by whitening clouds and by putting reflectors in space between earth and sun. The latter seems difficult to reverse and perhaps a very last resort. But whitening clouds can be quickly halted. It involves putting sulphur aerosols into the clouds in amounts that are trivial compared with the effects of either volcanic eruptions or coal burning worldwide. Or injecting saltwater micro-particles into ocean clouds which, whitened, then rain slightly salty water back into the oceans.

Amazing though it may seem, these apparently hopeful options are opposed by NGOs that seem more willing to run the risk of climatic catastrophe than deviate from the emissions reductions gospel. Their concern seems to be that geo-engineering will result in relaxed pressure to reduce emissions, which neglects the reality that more ambitious commitments will obviously go with increased capability to mitigate. They even oppose research, unlike Holdren's "it's got to be looked at".

The British researcher Tim Lenton uses the term geo-engineering to mean any way of cooling the earth that is not emissions reductions (even growing trees, which is included under the Kyoto protocol). His definition puts me – somewhat to my surprise – among the ranks of geo-engineers, as I have long advocated widespread tree-planting programmes, such as those initiated by the Nobel Peace laureate Wangari Muta Maathai, founder of the Green Belt Movement, which has planted more than 30m trees across Kenya.

• Peter Read is an honorary research fellow at the Centre for Energy Research, Massey University, New Zealand

[Note: My thoughts (submitted as a comment) are:

Peter,

I agree that tree plantations for charcoal feedstock is an excellent idea with one IMPORTANT caveat — there must be a firm incontrovertible rule against cutting natural forests for feedstock and/or triggering land use changes that result in increased deforestation. If this is not done, the sequestration gains of biochar will be negated by losses in the natural forest carbon sink.

Geo-engineering is a scary term because because it often focuses on single variable in reductionist and non-holistic ways. This might be corrected if the the grand schemers were to demonstrate how they are going to preserve natural ecosystem services such as those provided by remnant standing forests.]

[NOTE: This post with the comment has been syndicated at re:char which is a great site for keeping up with biochar developments. So, check it out.]

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